I've only ever played a defender, and that was more than a decade ago. As an outsider looking in, though, avengers seem like crappy monks. Whereas the avenger has some huge damage moves, the monk can achieve roughly the same effect by intensifying. Instead of one big move he gets a few rounds of super-juiced melee.

Fun thought exercise: how would Erhiadkeb's player fare playing an avenger? We've seen what he can do with champion and monk. He was actually considerably less deadly with the monk, but part of that may have been due to different priorities for the character. That, and monks not being able to extract as much benefit from top-shelf gear, e.g. eagle-inscribed staff, bal'talon, defiance, etc.